Crystallite size determinations for melt-spun FeNdB permanent magnet alloys

Abstract

Rapid solidification and subsequent processing are now a well-established route to the formation of FeNdB magnets. It is believed that an ultrafine grain size plays a major role in promoting high coercivity in this material. Crystallite size determinations have been made for as-cast melt-spun FeNdB ribbons of two composition types using X-ray diffraction peak-broadening analysis and transmission electron microscopy. The variation in crystalline size with ribbon thickness has been investigated for material cast onto copper and chromium roll surfaces. The magnetic properties _iH_C, B_r and (BH)_max were examined in order to determine the dependence on particle size. Additionally, overquenched, largely amorphous ribbon has been annealed to induce devitrification to various crystallite sizes and the evolution with time was examined in order to establish the optimum conditions for good magnetic properties.